The present invention relates to unsaturated polymer resin compositions and more particularly to stabilized unsaturated polymer resin compositions which include a cure promoter agent and methods of using the same.
Vinyl ester resins exhibit several desirable properties, including superior chemical resistance and excellent electrical and thermal-insulation properties. Such resins are industrially important in the manufacture of reinforced plastic components, boat hulls, fireproof molded articles, linings, paints, coating compositions, tanks, vessels, scrubbers, smoke stacks, pipe linings and other composite materials. These resins are generally prepared and mixed with a polymerizable monomer such as styrene, in order to reduce their viscosity. When cured, the styrene becomes a part of the resin system to produce a rigid cross-linked structure with desirable properties.
Tertiary aromatic amines are widely used as cure promoters or accelerators for unsaturated resins, including vinyl ester reins, in the presence of peroxide initiators. Exemplary tertiary amines useful as cure promoters include, for example, N,N-dimethylaniline (DMA), N,N-diethylaniline (DEA), N,N-bis-(2-hydroxyethyl)-m-toluidine, N,N-bis-(2-hydroxyethyl)-p-toluidine (HEPT), and N,N-dimethyl-p-toluidine (DMPT).
Some unsaturated polymer resin systems can be pre-formulated with the cure promoter or accelerator to yield a xe2x80x9cpre-promotedxe2x80x9d resin system. A common problem encountered with pre-promoted systems, however, is a decrease in storage stability or shelf life. The reaction times for gelling and subsequent curing of these systems tend to drift over a period of time, a phenomenon referred to as xe2x80x9cgel-time drift.xe2x80x9d The variations in gel time are typically measured as the difference between a gel-time after a period of storage and a gel-time just after formulation of the resin system. Usually, storing pre-promoted unsaturated polymer resin systems, particularly vinyl ester resin systems, for long periods results in longer gel or curing times. Such variations are problematic, particularly for applications requiring predictability of gel-time.
The present invention is directed to curable, pre-promoted unsaturated polymer resin systems that exhibit improved shelf stability and reduced gel-time drift. The pre-promoted systems of the invention generally include an unsaturated polymer resin, such as a vinyl ester resin, and a cure promoter capable of increasing storage stability or shelf life and also reducing or minimizing gel-drift thereof. Further, the pre-promoted systems exhibit improved shelf stability without an unduly adverse effect on cure rates. That is, the cure promoters can provide the apparent contradictory properties of improved storage stability with minimized gel-time drift coupled with fast cure speeds. Further, the promoters can provide fast cure rates at room temperature, and below.
The cure promoter can be a tertiary aromatic amine of the formula (I): 
wherein:
each A is independently selected from the group consisting of linear or branched C1 to C20, preferably C1 to C6, alkyl; C3 to C20, preferably C3 to C6, cycloalkyl; and functionalized linear or branched C1 to C20 alkyl comprising a heteroatom, with the proviso that both As are not linear or branched C1 to C20 alkyl; and
R5, R6, R7, R8, and R9 are each independently selected from the group consisting of H, linear or branched C1 to C20, preferably C1 to C6, alkyl, C3 to C20, preferably C3 to C6, cycloalkyl, and C1 to C20, preferably C1 to C6, alkoxy.
In various advantageous embodiments of the invention, at least one A can be functionalized linear or branched C1 to C20 alkyl comprising a heteroatom. In one aspect of this embodiment of the invention, at least one A can be linear or branched C1 to C20, preferably C1 to C6, alkyl or C3 to C20, preferably C1 to C6, cycloalkyl, and the other A can be functionalized linear or branched C1 to C20 alkyl comprising a heteroatom. In yet another aspect of this embodiment of the invention, both As can be functionalized linear or branched C1 to C20 alkyl comprising a heteroatom.
In yet another advantageous embodiment of the invention, at least one A is: 
wherein:
R2 is H, linear or branched C1 to C20, preferably C1 to C6, alkyl, or C3 to C20, preferably C3 to C6, cycloalkyl, wherein said C1 to C20 alkyl or C3 to C20 cycloalkyl is optionally substituted at the C1 or C3 position, respectively, by X as defined below;
R3 and R4 are each independently selected from the group consisting of H, linear or branched C1 to C20, preferably C1 to C6, alkyl, and C3 to C20, preferably C3 to C6, cycloalkyl; and
X is OH, OR1, CN, OC(O)R1, O[(CH2)mO]nH, O[(CH2)mO]nR1,[(CH2)m O]nH, [(CH2)mO]nR1, or NC(O)R1, wherein at least one H of each (CH2)m group can be optionally substituted with straight chain or branched C1-C20 alkyl, m=1 to 6, n=1 to 6, and each R1 is independently linear or branched C1 to C18 alkyl or C3 to C18 cycloalkyl. In one particularly advantageous aspect of the invention, the other A can be methyl and R7 can be linear or branched C1 to C6 alkyl, C3 to C6 cycloalkyl or C1 to C6 alkoxy.
Alternatively, in this aspect of the invention, each A can be 
wherein R2, R3, R4, and X are each as defined above.
In currently preferred embodiments of the invention, the cure promoter can be a tertiary aromatic amine of the formula (II): 
wherein:
R1 is linear or branched C1 to C6 alkyl or C3 to C6 cycloalkyl;
R2 is H, linear or branched C1 to C6 alkyl, or C3 to C6 cycloalkyl, wherein said C1 to C6 alkyl or C3 to C6 cycloalkyl is optionally substituted at the C1 or C3 position, respectively, by X as defined below;
R3 and R4 are each independently selected from the group consisting of H, linear or branched C1 to C6 alkyl, and C3 to C6 cycloalkyl;
R5, R6, R7, R8, and R9 are each independently selected from the group consisting of H, linear or branched C1 to C6 alkyl, C3 to C6 cycloalkyl, and C1 to C6 alkoxy; and
X is OH, OR1, CN, OC(O)R1, O[(CH2)mO]nH, O[(CH2)mO]nR1, [(CH2)m]nH, [(CH2)mO]nR1, or NC(O)R1, wherein at least one H of each (CH2)m group can be optionally substituted with straight chain or branched C1xe2x80x94C20 alkyl, m=1 to 6, n=1 to 6, and each R1 is independently linear or branched C1 to C18 alkyl or C3 to C18 cycloalkyl.
Particularly preferred are compounds of the following formula 
wherein
R2 is H, linear or branched C1 to C6 alkyl, or C3 to C6 cycloalkyl, wherein said C1 to C6 or C3 to C6 cycloalkyl is optionally substituted at the C1 or C3 position, respectively, by X as defined below;
R3 and R4 are each independently selected from the group consisting of H, linear or branched C1 to C6 alkyl, C3 to C6 cycloalkyl, and C1 to C6 alkoxy;
R7 is linear or branched C1 to C6 alkyl, C3 to C6 cycloalkyl or C1 to C6 alkoxy; and
X is OH, O[(CH2)mO]nH, or [(CH2)mO]nH, wherein at least one H of each (CH2)m group can be optionally substituted with straight chain or branched C1-C6 alkyl, m=2, and n=1 to 6.
The cure promoters of Formula (I), alone, in mixtures with one another, or in mixtures with other cure promoters, are particularly advantages for use with vinyl ester resins. Vinyl ester resins typically are not pre-promoted, due to the gel-time drift of such systems in the presence of conventional cure or accelerating promoters such as metal salts, e.g. cobalt naphthenate, N,N-dimethyl aniline, or N,N-dimethyl-p-toluidine.
The compound of Formula (I) may be added to the unsaturated polymer resin system between steps of formulation of the resin system or after all formulation steps are completed. Generally the compound of Formula (I) is added to the unsaturated polymer resin system in an amount effective to provide a promoted unsaturated polymer resin system having a gel-time drift which is lower than the gel-time drift of a counterpart unsaturated polymer resin with a promoter system lacking the compound of Formula (I).
The compound of Formula I may be added to restore the activity of a resin system which has been pre-promoted with conventional promoters and has already undergone gel-time drift. Gel times will then exhibit reduced drift from their restored activity. By comparison, adding conventional promoter will restore activity, but gel times will again drift.
The present invention also provides compositions that include the cure promoter of Formula (I) with the unsaturated polymer resin and a cure initiator, as well as processes for using the same.
Some of the features and advantages of the invention having been stated, others will become apparent from the detailed description which follows, and the accompanying drawings which form a part of the original disclosure of this invention, and in which:
FIGS. 1, 2, 3 and 4 are graphs illustrating gel and cure times, respectively, in minutes for a vinyl ester resin as a function of shelf aging (in weeks).